<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>加法计算</title>
    <script src="./../lib/jquery-3.7.0.js"></script>
</head>
<body>
<label>
    <input type="text" size="3">+
</label>
<label>
    <input type="text" size="3">=
</label>
<label>
    <input type="text" size="3">
</label>
<script type="text/javascript">
    $("input").eq(1).change(function () {
        let inputs = $("input");
        let number_1 = inputs.eq(0).val() - 0;
        let number_2 = inputs.eq(1).val() - 0;
        inputs.eq(2).val(number_1 + number_2);
    })
</script>
</body>
</html>